Random Access Control And Optimization For Machine Type Communication Device

Machine type communication devices (MTCDs) exchange data with each other over cellular networks is defined as machine to machine (M2M) communication. It has a massive number of devices, small-sized data transmission and many diverse applications. M2M communication is widely applied to smart metering, e-health, environmental monitoring and so on, which has a promising market in the future. However, the current cellular networks are designed for human to human (H2H) high speed downlink service, not suitable for M2M communication. On the one hand, a massive number of event-triggered MTCDs initial random access procedure in PRACH (Physical Random Access Channel) would cause serious collision, decreasing the success access probability. Additionally, in an uplink M2M communication, machine type communication device (MTCD) first performs contention-based random access (RA) procedure by preamble transmission in physical random access channel (PRACH), then transmits the data in physical uplink shared channel (PUSCH) after completing RA procedure successfully. A massive number of different applied MTCDs are characterized by small-sized data transmission. In this case, if MTCD employs the cellular networks communication way that MTCD establishes a random access link and transmits the information data afterwards, it will cost a highly signaling overhead and decrease the resource utilization. While the ratio between PRACH resource and PUSCH is mismatch would decrease the number of successful accesses. Therefore, this dissertation mainly focuses on the random access procedure of MTCD, and studies the serious collision problem caused by massive random access attempts and the resource allocation problem created by small-sized data transmission.To increase the success access probability in massive machine type communication devices (MTCDs) initialized uplink random access simultaneously, a preamble source division and ACB (access class barring) access congestion control strategy is proposed. In this scenario, the number of newly arrived MTCDs is far less than the number of backlog MTCDs. The base station (BS) can distinguish new MTCDs from backlog MTCDs by preamble division during the access procedure. Therefore, the BS can estimate the number of new MTCDs merely to calculate the number of total MTCDs, and reduce the estimation error, guarantee that the system parameters are closer to the optimum value. Additionally, we divide the preamble resource based on the number of estimated new MTCDs and backlog MTCDs, and configure different access parameters for those MTCDs by ACB strategy, optimize the number of access attempt to decrease the preamble collision probability. Simulation results demonstrate that the proposed access optimization scheme can increase the success access probability, while decrease the access delay and average service time.To increase the number of success access MTCDs in massive M2M communications characterized by small-sized data transmission, we apply ACB scheme and sparse code multiple access (SCMA) technique jointly, and optimize the ratio between PRACH (Physical Random Access Channel) resource and PUSCH (Physical Uplink Shared Channel) resource, the access parameter and the length of SCMA codeword. Here, we employ ACB scheme to control the massive random access attempts during preamble transmission in PRACH, and optimize the number of accesses to decrease the preamble collision probability and increase the success access probability. Additionally, the system can be overloaded using SCMA technique to accommodate more MTCDs to transmit small-sized data efficiently. Therefore, the BS allocates the SCMA codebook resource in PUSCH to those MTCDs with successful preamble transmission. To increase the number of success access MTCDs, a joint PRACH and PUSCH resource allocation optimization problem is formulated. Finally, we propose a detailed algorithm to solve the optimization problem, and optimize the ratio between PRACH and PUSCH, the access parameter and the length of SCMA codeword. Simulation results show that the proposed scheme can decrease the preamble collision probability efficiently, and increase the number of successful accesses and the PUSCH resource utilization even in the overload scenario.